Method of making insulated wire



1954 F. H. NICOLL ET A1. 3 7

METHOD OF MAKING INSULATED WIRE Filed June 29, 1949 FEEDER/0K H M00443;0A v/0 W fPSTE/N C ZITORNEY 5 Patented Got. 19, 1954 METHOD OF MAKINGINSULATED WIRE Frederick H. Nicol! and David W. Epstein, Princeton, N.J., assignors to Radio Corporation of America, a corporation of DelawareApplication June 29, 1949, Serial No. 102,092

5 Claims.

The present invention relates to improvements in methods of makinginsulated Wire and more directly, although not necessarily limitedthereto, to a method of making electrically insulated Wire suitable forconstructing close-wound coils of a type adapted for us at hightemperatures.

More particularly, the present invention deals with improvements in themanufacture of close- Wound electrical coils in which the individualturns oi the coils are to be insulated from one another and in whichthere is to be included substantially no impurities capable of adverselyaffecting high vacuum systems under conditions of elevated temperatures.

lhe present invention is further concerned with the method of makingelectrical coils suitable for inclusion in the vacuum envelopes ofelectronic discharge devices such as described, for example, in a copending application by D. W. Epstein et al., Serial No. 195,924, filedJuly 21, 1949, new Patent Number 2,542,493.

The use of insulated electrical conductors in high vacuum systems isquite common in the electrical art. For instance, in the interconnectionof various electrodes of complex electronic discharge tube structure, asfound, for example, in image orthicon television pick-up tube, it issometimes desirable to use insulated wire of one form or another. Insuch cases, the insulated Wire generally takes the form of a simpleelectrical conductor covered by a ceramic or glass sheathing, either inwoven or solid tubular form, which covering is inherently immune to thehigh temperatures employed in the manufacture of the electronic device.

As will be realized, the heat immunity of the insulated wire inelectronic discharge tub vacuum systems is quite important since anycomponent of the insulation, oxidizable or decomposable by extremetemperature, will tend to infect the desirably pure vacuum within thedischarge tube envelope. More particularly, if such decomposedinsulation components, formed during the well known heating ordegassing0f the electron tube envelope, should find residence on the dischargetube cathode surface serious damage to the cathode emissioncharacteristics could also result.

Moreover, as described in the patent above referred to, it is sometimesdesirable to include in a high vacuum electron discharge tube system aclose-wound electrical coil used for the inductive pick up ofelectromagnetic energy later to be rectified and used as electrodepolarizing potentials. Such a coil is made integral with theelecconductor.

tron tube structure during its manufacture is necessarily subjected tothe high degassing temperature of the discharge tube during its latterphases of construction. The coil, being preferably as small as possible,yet utilized for the generation of rather high peak voltages, sets forthquite severe insulating requirements, which requirements must be metwithout introducing into the coil structure elements detrimental to tubedegassing process. initial efforts in obtaining suitable coilarrangements led to the trial of numerous glass insulated wire types,the glass being chosen such as to be substantially immune to thenecessary high temperature. However, it is found that in the manufactureof glass-covered wire, as well as many other types of wire characterizedby their heat resistant in sulation, an adhesive or binder is placed onthe wire conductor to properly hold the heat resistant insulationmaterial to th conductor. Accordingly, at the higher degassingtemperatures encountered in electron tube manufacture, the adhesivesused for such a purpose are vclatilized or oxidized and contaminate theenvelope.

It therefore a purpose of the present inven tion to provide a novelmethod for making electrically insulated wire having a maximuminsulation characteristic with minimum size require- ;ments, yetembracing no constructional elements ing an electrical coil suitable lorhigh vacuum use wherein the coil may be subject to high operatingtemperatures and wherein the desired operating envior cnment is to bekept free of contamination.

In realizing the above objects, the present irrvention contemplates thefabrication of an insulated Wire by coating a wire conductor with anadhesive material suitable for conforming an insulating material to theouter surface of the The adhesive material, although be ing inherentlyadversely affected by higher temperature operation, does, at lowertemperatures, permit effective application or" the insulating materialwhich is, according to the present invention, necessarily immune to hightemperature conditions under which the wire is to be normally employed.The wire, with the adhesively-held insulation thereon, is then heated tooxidize or volatilize the adhesive binder, the products of such volatiization or oxidization being carried away by forced air or othersuitable cleansing aceazls 3 processes. The resulting wire thencomprises nothing more than an electrical conductor surrounded by a veryclosely associated insulation having a high degree of heat immunity withno construction elements likely to contaminate high vacuum systems inwhich the wire may find use.

Various modes of carrying out the present invention, as Well as numerousother objects and advantages thereof will become apparent to thoseskilled in the art through a perusal and understanding of the followingspecification, especially when considered in connection with theaccompanying drawings in which:

Figure 1 illustrates a very common use of wire in a vacuum system inaccordance with prior art technique;

Figure 2 illustrates a close-wound electrical coil of a type to whichthe present invention may be advantageously applied;

Figure 3 shows an electrical insulated conductor of the glass-insulatedtype before being fully treated in accordance with the presentinvention;

Figure 4 is the same glass-insulated conductor shown in Figure 3 afterhaving been fully processed according to the present invention;

Figure 5 shows an electrical coil of the form illustrated in Figure 2but constructed in accordance with the present invention therebypermitting its successful employment in the illustrated vacuum envelope.

Referring now to Figure l of the drawings, there is shown, only by wayof illustration, a typical prior art arrangement employing an electricalconductor ill in a vacuum chamber I2. Such an arrangement readily lendsitself for use as an electric lamp or heating device and, as such, theconductor Ii] may be coiled with such a low pitch that insulationbetween adjacent turns is not required.

However, should the coil 14 of Figure 2 be employed it is evident thatsuitable insulation around the wire would be necessary to preventshorting of adjacent turns. As stated above, such insulation in priorart arrangements may conveniently take the form of glass spaghetti,plastic sheath or other easily formed insulating materials. However,should the coil M be designed for use in a vacuum envelope such as l2,in which other elements, such as electron discharge tube structure, areto be situated, the chamber 12 would have to undergo suitable degassingbefore the seal l6 of the chamber was closed. This degassing processgenerally requires heating of the envelope and the structure within thesame, to temperatures in the neighborhood of 500 C. Obviously,insulation of the coil 14 must then be of a type which will withstandthis higher temperature. This indicates the desirable use of a glasstype of insulation.

As is well known, however, in the wire-making art, glass insulated wire,such as Vitro-tex, pres ently manufactured by the Anaconda Wire andCable Corporation of New York city or Single Glass mamel Wiremanufactured by the Wheeler Wire Company of Bridgeport, Connecticut,necessarily employs around the surface of the conductor abinder orenamel on which to wind the glass insulated material. Such glass-coveredwire so intimately associates the glass insulation with the outersurface of the conductor that a considerable saving in the spacerequired by a coil of a given number of turns is made possible over andabove the use of glass or other type of insulating sheathing, It hasbeen found though that this adhesive binder material, on which the glassinsulation is wound, tends to decompose by volatilization or oxidationduring the degassing or heating proces and upon sealing of the vacuumchamber l5 and cooling thereof, pre sents a very serious form ofcontamination in the chamber. Sometimes the volatilized adhesivematerial tends to condense upon cooling on portions of the structurewithin the vacuum chamber adversely affected thereby.

According to the present invention, the contaminating effects on theadhesive binder employed to initially conform the heat-resistantinsulation to the conductor may be eliminated. This is done by heatingin air or other suitable atmospheres the wire at a temperature at leastas high as the temperature to which it is to be subjected in theevacuated chamber. This heating is continued until all of the oxidizableor volatilizable and otherwise decomposable materials constituting theadhesive binder are driven ofi thereby leaving nothing but the glassinsulation surrounding the wire conductor.

The effects of this process are illustrated more clearly by Figures 3and 4 which respectively show a conductor, such as the glass enamelvariety, before and after treatment according to the present invention.In Figure 3, the conductor 18 has an adhesive binder 20 to which thethreaded glass insulation 22 adheres when woven onto the conductor. Asnoted, this binder 2D is considered by the wire-making industry asnecessary in successfully applying an insulation of the woven glassvariety. After prolonged heating and oxidation such as, for example, inopen air at high temperatures, the binder 20 is driven off or decomposedto leave nothing but the woven glass insulation 22 surrounding the wireconductor i 8, as shown in Figure 4.

After removing the binder 20, the wire or the coil, such as 24, intowhich the wire may be formed, as shown in Figure 5, is in suitablecondition for placing in a vacuum chamber, such as 26, to be heated anddegassed in accordance with conventional practice.

It is noted that, as shown in Figures 2 and 5, an appropriate type ofcement or ceramic binder 28 may be applied to aid in holding the turnsof the coil together, thereby making its manipulation somewhat easier.It will be realized that provided the porosity of the insulation 22 wassufficiently great, the binder 20 could be removed subsequent to themanufacture of the insulated Wire by submerging the wire or coil in asolution containing a dissolving or decomposing agent for the bindingmaterial. In any event, it is generally found that, although the coilinto which the wire is to be formed may be wound subsequent to theremoval of the binder 20- by heating or otherwise, it is generallydesirable to form the coil prior to the removal of the binder.

It is moreover manifest that a variety of insulating material may beemployed for such application in heated vacuum systems provided thematerial itself will not be adversely affected by the higher degassingtemperature. Mica or suitable forms of ceramics could conceivably beused for this purpose, As the art progresses, other insulating materialssuitable for such high temperature Work will undoubtedly becomeavailable and fall within the useful scope of the present invention.

Having thus described my invention, what I claim is:

1. The method of making an insulated electrical conductor suited for usein elevated temperature environments comprising the steps of coating anelectrical conductor with an adhesive binder inherently decomposable bythe elevated temperatures to form readily mobile decomposition productsadverse to the normal operating conditions of the conductor, coveringthe conductor, through the aid of the adhesive under lowered temperatureconditions, with a glass-insulating material having a meltingtemperature below the predetermined elevated temperature environments,heating the so-formed insulated conductor to a temperature permittingdecomposition of the adhesive, and removing the products of adhesivedecomposition from between the conductor and insulating material.

2. The method according to claim 1 wherein the adhesive is readilyvolatilized and oxidized to form vaporous products of decomposition andwherein the removal of the adhesive decomposition products comprises theventilization of the wire during heating in an atmosphere permittingready oxidation and volatilization of the adhesive.

3. The method of making an insulated electrical conductor from alaminated assembly comprising an electrical conductor and a covering ofrefractory electrical insulating material bonded thereto by an adhesivematerial which decomposes at elevated temperatures, which comprises thestep of heating such assembly to a temperature sufiicient to decomposesaid adhesive material but insufficient to affect said refractorymaterial.

4. The method as defined by claim 3 wherein said insulating materialcomprises glass fibers.

5. The method of making an insulating electrical conductor from alaminated assembly comprising an electrical conductor, a. coatingthereon of adhesive material which decomposes under certain treatmentand a covering of electrical insulating material secured to suchconductor by said adhesive, said covering being relatively impervious tosaid certain treatment, which comprises the step of subjecting saidassembly to said certain treatment whereby to decompose said adhesivematerial.

References Cited in the file of this patent UNITED STATES PATENTS

1. THE METHOD OF MAKING AN INSULATED ELECTRICAL CONDUCTOR SUITED FOR USEIN ELEVATED TEMPERATURE ENVIRONMENTS COMPRISING THE STEPS OF: COATING ANELECTRICAL CONDUCTOR WITH AN ADHESIVE BINDER INHERENTLY DECOMPOSABLE BYTHE ELEVATED TEMPERTURE TO FORM READILY MOBILE DECOMPOSITION PRODUCTSADVERSE TO THE NORMAL OPERATING CONDITIONS OF THE CONDUCTOR, COVERINGTHE CONDUCTOR, THROUGH THE AID OF THE ADHESIVE UNDER LOWEREDTERMPERATURE CONDITIONS, WITH A GLASS-INSULATING MATERIAL HAVING AMELTING TEMPERATURE BELOW THE PREDETERMINED ELEVATED TEMPERATUREENVIRONMENTS, HEATING THE SO-FORMED INSULATED CONDUCTOR TO A TEMPERATUREPERMITTING DECOMPOSITION OF THE ADHESIVE, AND REMOVING THE PRODUCTS OFADHESIVE DECOMPOSITION FROM BETWEEN THE CONDUCTOR AND ISULATINGMATERIAL.